Hydrothermal synthesis, crystal structures, and X-ray photoelectron spectroscopy of lead tellurium(iv) and tellurium(vi) oxycompounds: Ba3PbTe6O16 and Na2Pb9(μ6-O)2(Te2O10)2

Abstract

An exploratory study of the lead-tellurium-oxygen phase space led to two new compounds, Ba₃PbTe₆O₁₆ (BPTO) and Na₂Pb₉(μ₆-O)₂(Te₂O₁₀)₂ (NPTO), which were synthesized under hydrothermal conditions at 550 °C and 210 °C, respectively, and characterized by single-crystal X-ray diffraction, infrared and X-ray photoelectron spectroscopy. BPTO adopts a layer structure. The Te⁴⁺ cation in BPTO is bonded to four oxygen atoms at about 2.0 Å with two more oxygens at about 3.0 Å. The seesaw-shaped TeO₄ units share corners to form 2D layers containing six-membered rings and the Ba²⁺ and Pb²⁺ cations are situated in the interlayer region. The structure of NPTO contains dimers of edge-sharing Te⁶⁺O₆ octahedra, which are connected through five-coordinate Pb²⁺ cations. A unique six-coordinate O atom is at the center of the octahedron formed by five Pb²⁺ and one Na⁺ cations. BPTO is one of the few metal tellurites which were synthesized under supercritical hydrothermal reaction conditions. The Pb²⁺ cation in NPTO shows pronounced stereochemical effects of the lone electron pair. In contrast, BPTO shows no stereochemical evidence of the inert pair.